This invention relates generally to combustors and, more particularly to a method and apparatus for decreasing combustor acoustics.
Air pollution concerns worldwide have led to stricter emissions standards both domestically and internationally. Pollutant emissions from industrial gas turbines are subject to Environmental Protection Agency (EPA) standards. These standards regulate the emission of oxides of nitrogen (NOx), unburned hydrocarbons (HC), and carbon monoxide (CO). With the continuing concerns for the environment, the trend toward more stringent emission standards can be expected to continue.
In general, engine emissions fall into two classes: those formed because of high flame temperatures (NOx), and those formed because of low flame temperatures that do not allow the fuel-air reaction to proceed to completion (HC & CO). In at least some engines, water is injected into the combustor to facilitate reducing flame temperature and thus (NOx) emissions. Alternatively, dry low emission (DLE) combustors are designed to facilitate reducing (CO) and (NOx) emissions without the use of water injection. However, to facilitate low emissions, the DLE combustor is run at lean fuel-air ratios which require uniform dispersion of fuel throughout the combustor. More specifically, such combustors include fuel delivery systems that circumferentially stage fuel flows through the premixers to facilitate evenly dispersing fuel throughout the combustor.
However, one problem that may arise with the DLE combustor and its associated fuel delivery system is the potential for high acoustics in the combustor. Combustor acoustics can result from several mechanisms, such as may be associated with thermally induced pressure disturbances resulting from instabilities or unsteadiness in heat released from the lean premixed flame. Such thermal instabilities can combine with natural acoustics generated within the combustor to produce high energy acoustic vibrations which over time may damage the combustor and other components. As a result, high combustor acoustics may limit the operation of the combustor.